The invention relates to a magnetic head, and more particularly, to a magnetic head for use in a tape recorder, video tape recorder (VTR) etc., in which a high density recording is achieved by establishing a remanence in the direction of thickness of a magnetic record medium such as a magnetic tape.
Ordinarily, the technique to record an information signal on a magnetic record medium such as magnetic tape generally comprises bringing a magnetic head into contact with the surface of the medium to establish a remanence in a direction parallel to the surface of the medium. According to this technique, the head has its poles located opposite to each other with a narrow air gap therebetween so that a leakage flux from the gap is bypassed through the medium. Because the leakage flux passes through the medium in a direction parallel to its surface, the magnetizable material contained in the medium is magnetized in a direction parallel to the surface of the medium, with its remanence defining a magnetic recording. With the described magnetic recording technique, it is known that considerations of the air gap of the magnetic head and the frequency of the signals being recorded impose a limitation on the recording density of the information signal.
Recently, a variety of recording techniques have been proposed which drastically improve the recording density by a so-called vertical magnetization scheme in which a remanence is established in the medium in a direction perpendicular to the surface thereof or in the direction of its thickness. This technique employs a magnetic record medium having an easy axis of magnetization in a direction perpendicular to the surface. Referring to FIG. 1, there is shown a magnetic record medium 6 comprising a base film 6c of polyester, for example, carrying an upper layer 6b of high permeability material and a top layer 6a coated thereon which is formed of a magnetizable material having an easy axis of magnetization in a direction perpendicular to the surface.
FIG. 1 also shows a magnetic head 1 which may be used for recording a signal in such medium. Specifically, the head 1 comprises a magnetic head core 2 of a magnetizable material such as ferrite which has an inverted U-configuration, and a coil 3 disposed thereon. The core 2 includes one limb 4 which has its free end tapered, with its end face defining a narrow rectangle which is elongate in a direction perpendicular to the direction of movement of the record medium and forming a pole 4a for recording and/or playback. This end face is adapted to be disposed in abutment against the medium. The core has its other limb 5 which has an increased thickness to present an increased cross-sectional area, thus reducing its reluctance.
In operation, when a signal current is passed through the coil 3 as the medium 6 moves to the left, as viewed in FIG. 1, relative to the head 1, flux 7 is produced within the core 2 as indicated by dotted line. The flux passes from the pole 4a vertically through the layer 6a and passes through the layer 6b in a direction perpendicular to the surface and returns to the limb 5, thus forming a closed magnetic path. It will be seen that as the flux passes vertically through the portion of the layer 6a which is located opposite to the pole 4a, a remanence is produced therein in a direction perpendicular to the surface, and because the pole 4a has a reduced width, a high flux density is produced. In a region of the layer 6a which is located opposite to the limb 5, the flux density is greatly reduced because of an increased area of the end face of the limb 5, and hence no substantial or effective magnetization occurs in this region of the layer 6a. As the medium 6 continues to move to the left relative to the head 1, a pattern of the remanence corresponding to the signal current is recorded in the top layer 6a, thus achieving a magnetic recording.
During the playback operation, the both limbs 4 and 5 have their end faces disposed in abutment against the medium 6, and latter driven to the left. The remanance recorded in the medium passes through a closed magnetic path including core 2, top layer 6a and the high permeability layer 6b, linking with the coil 3 to produce a playback current which varies in accordance with a variation in the remanence recorded in the top layer 6a of the medium with time.
In order to increase the recording density and the magnitude of remanence produced in the medium 6, it is desirable that the width l of the pole 4a be made as narrow as possible. In one instance, a width on the order of 0.1 micron may be required. However, it is very difficult to form a very narrow width of the pole 4a because of the mechanical properties of a magnetizable material such as ferrite, and if it is possible to achieve a precise machining, the pole 4a having such a reduced width is soon abraded or cracked, preventing its practical use.
FIG. 2 shows another form of conventional magnetic head 11. This head comprises a magnetic head core 12 having an inverted L-configuration, a record/playback pole 14 which is magnetically coupled with the free end of the horizontal arm of the core to present a generally inverted U-configuration therewith, and a coil 13 disposed on the core. The pole 14 is formed of a thick non-magnetic material 16 and a layer 17 of a magnetizable material having a greatly reduced thickness and which is formed as by sputtering, with the free end face of the layer 17 defining a record/playback pole face 17a. Vertical arm of the core 12 has an increased thickness to present an increased cross-sectional area to form the other pole 15 having a reduced reluctance. The formation of the layer 17 as by sputtering facilitates its manufacturing, and enables the thickness of the layer 17 to be reduced as desired. However, because the layer 17 remains exposed externally, it is susceptible to damage. Also there remains the disadvantage that the edge or corner of the free end of the layer 17 is apt to be cracked.